swift 2.1 Xcode database : thread1 EXC_BREAKPOINT

Question

I am developing an application that uses Xcode database for the first time. By following an online tutorial I got the idea how to do it step by step, but when I test the app I get runtime exception when it reaches the line which saves the data into the database.

This is the code I wrote so far, the idea is when a star button pressed the user information will be saved

        @IBAction func favPressed(sender: AnyObject) {

    let appDel:AppDelegate = (UIApplication.sharedApplication().delegate as! AppDelegate)
    let context:NSManagedObjectContext = appDel.managedObjectContext

    // here is where the app crushes:
    let newFav = NSEntityDescription.insertNewObjectForEntityForName("FavoriteUser", inManagedObjectContext: context) as! NSManagedObject

    newFav.setValue("" + userName, forKey: "uName")
    newFav.setValue("" + userEmail, forKey: "uEmail")
    newFav.setValue("" + userPhone, forKey: "uPhone")

    do{
    try context.save()
    }
    catch{
        print(error)
    }
    print("user saved to favs")
}

I have no idea why this is happening, and I don't know if this will be helpful but note that I used the Core Data into an existing big project. I have added the CoreData.framework and the required functions in the appDelegate.swift